This invention relates to a piston, particularly for internal combustion engines, comprising a head and a skirt having annular grooves therein to receive piston rings and gudgeon pin bores the bearing surfaces of which skirt come into contact with the bore of the cylinder in which it reciprocates lie on a generated surface which has an essentially circular or elliptical outer contour in all cross-sections vertical to the longitudinal axis of the piston, and in the longitudinal axis of the piston straight or curved generating lines.
It is known to make the outer contour of the generated surface in which the running surfaces of the piston lie deviate from a round or elliptical basic shape in cross-section. The generated surface also generally does not exhibit a straight course in the longitudinal direction of the piston. The pistons are instead generally barrel-shaped or convex in this direction.
The cross-section particularly of light metal pistons generaly have a round basic shape with superimposed ovalities. The small axis of ovality is always in the direction of the gudgeon pin. The difference in length between the large and small axes of ovalilty is generally of the order of 0.1-0.8 mm.
Pistons with a basic shape which is already elliptical in cross-section may also contain corresponding superimposed ovalities.
It is also known to shape the outer contour in the circumferential directiion on the thrust and anti-thrust sides of the piston differently, as shown for example in DE-AS No. 12 94 740. However, in the case of the different outer contours the two generatrices opposite each other in the connecting rod reciprocating plane run symmetrically to the longitudinal axis of the piston. Moreover, the cross-sectional contours are in mirror symmetry to the connecting rod reciprocating plane running through the longitudinal axis of the piston.
In addition to the above reference the most relevant prior art known in the applicant is as follows:
DE-PS No. 856 247 PA1 DE-PS No. 755 235 PA1 DE-OS No. 29 13 418 PA1 DE-OS No. 14 75 846 PA1 DE-AN No. A22663 XII/47 published Feb. 16, 1956 PA1 U.S. Pat. No. 34,63,957 PA1 Japanese Pat. No. 23 048-84